it all went well and only issue had is that the named dns failed to start and rest all even dovcot all started off.. and i installed ispconfig3 and as per the given details on the above pages. the dovecot failed as well and i had put the fix as per the information if it failed. But still then the same issue comes up. when i login to the cp and check it still says that the pop imap is offline and dns server is also offline. can you help me out. if i can get some step by step info on what is to be done, it would help me as i am nearing my deadline to launch the websites via this server.

Please check the logs in /var/log/, especially /var/log/maillog and /var/log/syslog (or /var/log/messages, not sure about the correct name on CentOS). Do you see any errors when you restart BIND and dovecot?

Restarting IMAP/POP3 mail server: dovecotLast died with error (see error log for more information): Time just moved backwards by 299 seconds. This might cause a lot of problems, so I'll just kill myself now. http://wiki.dovecot.org/TimeMovedBackwards
If you have trouble with authentication failures,
enable auth_debug setting. See http://wiki.dovecot.org/WhyDoesItNotWork
This message goes away after the first successful login.
.

root@srv1:~# service dovecot restart
Restarting IMAP/POP3 mail server: dovecotLast died with error (see error log for more information): Time just moved backwards by 299 seconds. This might cause a lot of problems, so I'll just kill myself now. http://wiki.dovecot.org/TimeMovedBackwards
If you have trouble with authentication failures,
enable auth_debug setting. See http://wiki.dovecot.org/WhyDoesItNotWork
This message goes away after the first successful login.
.

SMTP server is working, but emails sends from server with very long interval about 5-6 hours. What can do in this situation? Maybe do I need to configure cron for SMTP-server?